Goddess Durga is nature or prakriti - explains A Parthasarathy.
Uma is the consort of Shiva, the Lord of constructive destruction. Uma represents Prakriti (matter). The power of destruction has always to be associated with destructible matter in order that this power could manifest. In other words, destruction ceases to have any meaning without destructible objects. Lord Shiva has, therefore, chosen Uma to be his partner.
The god and goddess are the first self-revelation of the Absolute, the male being the personification of the passive aspect and the female, the activating energy (Shakti). Goddess Parvati (Uma) represents this Universal Power (Shakti). Uma and Parvati are her Maiden names; and Mrudani and Ambika are her post-marriage names.
The Goddess is also referred to as Annapurna meaning ‘Bestower of Food’ ‘Anna’, though translated as ‘food,’ has a wider connotation and includes all material objects/wealth, which are food for the five-sense organs. The Goddess is possessed of all types of ‘food’ to offer Her devotees.
All the three Goddesses together are represented by the fierce-looking Goddess Durga or Kali. She is shown in a fearful form. Kali is worshipped by a seeker to invoke the latent power of destruction and thereby annihilate all his negative tendencies and qualities which veil his Higher Self.
A Parthasarathy
Source – Excerpt from an article in Symbolism in Hinduism published by Chinmaya Mission